284 TEXT-BOOK OF PHYSIOLOGY 



The intra-ventricular pressure has been obtained by specially devised 

 manometers or tonometers or tono graphs, as they are variously termed, the 

 construction of which is such as to enable them to respond instantly to the 

 very rapid variations of the pressure which occur during the brief cardiac 

 cycle. One of the best is that of Hiirthle. This consists of a small metallic 

 tambour 5 or 6 millimeters in diameter, covered by a thin rubber membrane. 

 A small button resting on the membrane plays against an elastic steel spring, 

 by the tension of which the pressure of the blood is counterbalanced. The 

 movements of the membrane are taken up, magnified, and recorded by a 

 suitable lever. A long cannula is inserted into the right ventricle through 

 the jugular vein or into the left ventricle through the carotid artery. Both 

 cannula and tambour are filled with an alkaline solution to prevent coagula- 

 tion of the blood, and then made air-tight. The pressure of the blood in the 

 ventricle is thus transmitted by a liquid column to the tambour and to its 

 attached lever. With such a manometer a curve is registered similar to that 

 shown in Fig. 122. To obtain the absolute value of this curve in millimeters 

 of mercury it is necessary to graduate the instrument previously. An 

 examination of the curve shows that previous to the ventricular contraction 

 there is a very slight rise of pressure above that of the atmosphere, repre- 

 sented by the line o o. This may be due to the inflow of blood from the 

 auricle during the diastole. At o the pressure suddenly rises, passes quickly 

 to its maximum value, (2), which is maintained with slight variations for 

 some time, and then suddenly (3) begins to fall, and rapidly reaches the 

 line of atmospheric pressure, or even passes below it, becoming negative in 

 fact for a short period. A characteristic feature of this curve is the more 

 or less horizontal portion comprised between the points 2 and 3, marked 

 by several elevations and depressions, which has been termed the systolic 

 plateau. 



The Relation of the Intra-ventricular Pressure Curve to the Intra- 

 cardiac Mechanisms. By itself the curve of the intra-ventricular pressure 

 affords no indication as to events occurring within the heart: i.e., as to the 

 times during the systole, of (i) the closure of the auriculo-ventricular valves 

 and (2) the opening of the semilunar valves, or the times during the dias- 

 tole, of (3) the closure of the semilunar valves and (4) the opening of the 

 auriculo-ventricular valves. 



By registering the curve of pressure in the aorta simultaneously with the 

 curve of the pressure in the left ventricle (Fig. 122), and by comparing 

 these with the curve of the successive differences of pressure in these two 

 cavities as determined by the " differential manometer," it becomes possi- 

 ble to mark on the ventricular pressure curve the points at which the fore- 

 going events take place. 



As the outcome of many observations and determinations, the follow- 

 ing statements may be made: As a point of departure for a consideration 

 of the relation of the intra-ventricular pressure to the time of action of 

 the valves, the close of the ventricular systole may be conveniently 

 selected. 



During the period represented by the systolic plateau the blood is 

 passing from the ventricle into the aorta. Independent of the slight ele- 

 vations and depressions there is an absolute fall of pressure between the 

 beginning and the end of the plateau. There is also a corresponding fall 



